System for automatically decelerating rolling mills

ABSTRACT

DESCRIBED IS A SYSTEM FOR AUTOMATICALLY DECELERATING A ROLLING MILL FROM A HIGH SPEED TO A PRESET LOW SPEED SUCH THAT THE END OF A COIL BEING ROLLED APPROACHES THE BITE OF THE ROLLING MILL ROLLS WHEN THE PRESET LOW SPEED IS REACHED. AT THE SAME TIME, THE ROLLING MILL SCREWS ARE AUTOMATICALLY RAISED WHEN THE STRIP SPEED APPROACHES PRESET LOW SPEED TO PERMIT THE TRAILING END OF THE COIL TO PASS THROUGH THE MILL.

Jan. 12, 1971 s. s. HARBAUGH 3,553,992

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qQktwsb. A NQUM kwkum A United States Patent 3,553,992 SYSTEM FOR AUTOMATICALLY DECELERATING ROLLING MILLS Samuel S. Harbangh, Natroua Heights, Pa., assignor to Allegheny Ludlum Steel Corporation, Brackenridge, Pa., a corporation of Pennsylvania Filed Apr. 24, 1968, Ser. No. 723,813 Int. Cl. B21]: 37/00 US. Cl. 72-9 7 Claims ABSTRACT OF THE DISCLOSURE Described is a system for automatically decelerating a rolling mill from a high speed to a preset low speed such that the end of a coil being rolled approaches the bite of the rolling mill rolls when the preset low speed is reached. At the same time, the rolling mill screws are automatically raised when the strip speed approaches the preset low speed to permit the trailing end of the coil to pass rough the mill.

BACKGROUND OF THE INVENTION In the rolling of steel strip material, steel issuing from a coil passes through a rolling mill at a relatively high rate of speed during the major portion of the rolling process. However, when the end of the coil is reached, the mill must be decelerated to a lower speed; and just before the trailing end of the strip passes through the rolls, the rolling mill screwdown mechanism must separate the rolls to permit the trailing end to pass through. Otherwise, if the strip were not decelerated and'the rolls separated, extensive scouring and damage to the rolls could result.

In the past, deceleration of the mill and separation of the rolls were under the manual control of an operator Who usually observed that the end of the coil was approaching and then manipulated controls to slow down the mill. In many cases, however, the mill was decelerated before it was necessary resulting in a loss of production time; and, of course, there was always the possibility of operator error and damage to the rolls.

SUMMARY OF THE INVENTION As an overall object, the present invention seeks to provide a system for automatically decelerating a rolling mill just prior to the completion of rolling of a coil of steel passing through the mill.

More specifically, an object of the invention is to provide a system for automatically decelerating a rolling mill from a consideration of the length of coiled steel remaining on a payoff reel feeding into the mill, and the length of steel which will go by the entry X-ray gage as the mill is decelerating at a predetermined rate. Programmed deceleration at the aforesaid predetermined rate is initiated at the time the calculation finds the two lengths equal.

Still another object of the invention is to provide an automatic rolling mill decelerating system incorporating means for automatically raising the mill screwdowns prior to the time that the end of the strip passes through the mill.

In accordance with the invention, means are provided for producing, during a rolling operation, a first electrical quantity which is proportional to the length of material remaining on the mill payoff reel, means for producing, during a rolling operation, a second electrical quantity which is proportional to the length of material which will pass into the mill at a predetermined deceleration rate from a consideration of the exit velocity of the material issuing from the mill, means for comparing the first and second electrical quantities, and means coupled to the 3,553,992 Patented Jan. 12, 1971 ice comparing means for decelerating the mill at the aforesaid predetermined deceleration rate when the electrical quantities compared by the comparing means are the same.

Preferably, the first and second electrical quantities are digital signals produced by digital computers; however an analog system may be used in certain cases. In the usual case, the first and second electrical quantities are produced continually during a rolling operation; however it will be appreciated that it is only necessary for them to be produced just prior to the time that the mill Should be decelerated.

Further, in accordance with the invention, means are provided during deceleration of the mill for maintaining tension in the strip even though the trailing end of the strip leaves the payoff reel. Additional means are provided for detecting when the end of the strip leaves the payoff reel and for automatically raising the mill screws in order that the end of the strip can pass therethrough without damaging the rolls. All of this is accomplished without requiring any manual manipulations on the part of the operator.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

FIG. 1 is a schematic block diagram of one control system embodying the principles of the invention; and

FIG. 2 is a graph of mill speed versus time showing the manner in which the mill is decelerated in accordance with the system of 'FIG. 1.

Referring now to the drawings, and particularly to FIG. 1, a rolling mill installation is shown comprising three tandem stands A, B and C. Each stand includes upper and lower rolls 10 and 12. The lower rolls 12 are stationary; however the upper rolls 10 may be raised or lowered by means of screw mechanisms 14 each controlled by screw control mechanisms 16.

Each stand A, B or C is provided with a drive motor system, the drive motor for stand C being designated by the reference numeral 18. The drive motor 18 is energized from generator 20 which, in turn, is driven by a threephase synchronous motor 22. The generator 20 is provided with a field winding 24 connected to a generator control circuit 26; and circuit 26 is controlled along with the corresponding circuits for stands A and B by means of a master pilot regulator 28.

The strip material to be reduced in the mill issues from a payoff reel 30 and thence travels around the bridle rolls 32 and 34. From roll 34, the strip material passes beneath an X-ray thickness gage 36 and then under roll 38 before it passes between the bite of rolls 10 and 12 of stand A.

As will be appropriate, itis possible to compute, at any speed, the length of material which will pass through the mill before it stops at a given deceleration rate. Likewise, it is possible to compute the length of the material remaining on the payoff reel 30. When these two quantities are equal, the mill should start decelerating.

To calculate the length of steel remaining on the payoff reel, L, it is necessary to determine the inner coil diameter, DM, the outer coil diameter, D, and the steel thickness, G. The inner .coil diameter, DM, in most cases is controlled by mandrels on a previous process and is constant. However, if this quantity varied, it would be necessary to instrument the payoff reel mandrel such that the inner coil diameter could be continually measured. The thickness, G, is measured by the entry X-ray gage 36 and assumed to be the same throughout the coil remaining on the payoff reel. The outer coil diameter, D, is inconvenient to measure directly. Therefore, in the system shown, it is calculated from the payoff reel rotational where:

V =feet per minute, N=revolutions per minute, and D=inches.

Computer circuitry for computing the foregoing Equation 1 is identified in FIG. 1 by the reference numeral 40. The payoff reel rotational speed, N, is derived by means of a tachometer generator 42 connected to the mandrel for the payoff reel; and this value is averaged and stored in circuit 44 and continually applied to the computer circuit 40. Similarly, the entry velocity, V is derived from a tachometer generator 46 connected to a roll 48 in engagement with the moving strip material. The output of the tachometer generator 46, being proportional to the quantity, V is averaged and stored in circuit 50 and continually applied to the computer circuit 40. Hence, computer circuit 40 continually produces an electrical output on lead 52 which is proportional to D, the outer coil diameter.

The length, L, of the material remaining on the payoff reel 30 at any time can be calculated from the formula:

where:

D, DM and G=inches, and L=feet.

Computer circuitry for computing the foregoing Equation 2 is identified in FIG. 2 by the reference numeral 54. The output of computer circuit 40 comprising an electrical signal proportional to the quantity, D, is applied to the input of circuit 54 along with an electrical signal from X-ray gage 36 proportional to G and which is averaged and stored in circuit 56.

The length of material which will go by the entry X-ray gage 36 while the mill is slowing down at a predetermined deceleration rate is designated herein as SGB. In order to calculate this quantity, it is necessary to know the present entry speed, V and the time, TRT, it will take for the mill to decelerate. The quantity, SGB, can be calculated by the following formula:

(3) V XTRT SGB: 120

where:

V =feet per minute, and TRT =seconds.

The quantity, TRT, can be determined from the deceleration rate, RS, and the present exit velocity, V in accordance with the following formula:

( L TRT-RS where:

Vg=feet per minute, and RS=feet per minute per second.

to the computer circuit 58 where the quantity, TRT, is calculated.

The quantity, TRT, appearing on lead 68, is applied to computer circuit 70 along with the quantity, V from circuit 50. Computer circuit 70 computes Equation 3 given above; and when the quantity, SGB, from circuit 70 matches the quantity, L, from computer circuit '54, it is known that the mill should start decelerating. In this connection, the electrical signals proportional to L and SGB from circuits 54 and 70 are compared in comparator 72; and when they are the same they actuate the master pilot regulator 28 to decelerate the mill at a fixed rate, RS.

The manner in which the mill decelerates is shown in FIG. 2. Initially, it will be assumed that the mill is running at a normal speed of 1800 feet per minute. At time 1 the output of computer circuit 70 matches the output from computer circuit 54, indicating that the length of material remaining on the payoff reel 30 is equal to that length which will pass through the mill at the preset deceleration rate, RS. Accordingly, the mill decelerates until, at time t it has reached an intermediate velocity of 600 feet per minute. The mill continues to operate at 600 feet per minute until time i where the end of the strip material leaves the coiler 30.

With reference, again, to FIG .1, it will be seen that the coiler 30 is braked by means of a generator 74; and as soon as the end of the coil leaves the coiler, it decelerates very rapidly. This is detected as a fall in the output of the tachometer generator 42 by means of detector circuit 76. Detector circuit 76, in turn, causes the screw controls 16 to elevate the uper rolls 10; and at the same time it applies a signal via lead 78 to the master pilot regulator to further decelerate the mill to a speed of about 200 feet per minute which is reached at time t It is, of course, possible to decelerate the mill directly from 1800 feet per minute to 200 feet per minute; however due to variations in circuitry, the time at which the deceleration is started or the slope of the deceleration curve may vary. Accordingly, as a safety factor, the mill is decelerated in two steps. That is, it is first decelerated to 600 feet per minute and thereafter decelerated to 100 feet per minute at time 2 when the end of the strip material leaves the coiler.

It is desirable to maintain the tension in the strip material as long as possible, even though the end of the strip has left the coiler. Accordingly, a snubber roll 80 is provided on a rotatable arm 82. The arm 82 and the roll 80 carried thereby may be moved up into the dotted line position shown, where the roll is in engagement with the strip on the lower bridle roll 32, by means of a pneumatic or hydraulic cylinder 84. The cylinder 84, in turn, is controlled by means of a valve *86 actuated by solenoid 88. The solenoid 88 is connected to the output of a flipflop circuit 90 which, in turn, is caused to change its stable states and energize solenoid 88 by the output from a detector 92. The detector 92 is connected, as shown, to the tachometer generator 62 which will cause the detector 92 to actuate flip-flop circuit 90 when the exit speed falls to 600 feet per minute at time t This, of course, occurs before the trailing end of the strip leaves the payoff reel.

The present invention thus provides a means for automatically decelerating a rolling mill and for raising the rolling mill screws without requiring any attention on the part of the operator. Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

I claim as my invention:

1. Apparatus for automatically decelerating a rolling mill from a high speed to a preset low speed before the end of a coil of strip material issuing from a payoff reel passes through the mill, comprising means for continually measuring the actual gage of strip material entering the mill, means for producing during a rolling operation a first electrical quantity which is proportional to the length of material remaining on the payoff reel, said first electrical quantity being produced from a consideration of the velocity of strip material entering the mill, the actual measured gage of material entering the mill and the rotational speed of said reel, means for producing during a rolling operation a second electrical quantity which is proportional to the length of material which will pass into the mill at a predetermined deceleration rate, said second electrical quantity being produced from a consideration of the exit velocity of the strip material issuing from the mill and the velocity of strip material entering the mill, means for comparing said first and second quantities, and means coupled to said comparing means for decelerating the mill at said predetermined deceleration rate when the electrical quantities compared by said comparing means are the same.

2. The apparatus of claim 1 wherein said decelerating means initially decelerates the mill from said high speed to an intermediate speed which is above said preset loW speed, and including means operable when the trailing end of the strip material leaves the payofi reel for decelerating said mill from said intermediate speed to said preset low speed.

3. The apparatus of claim '2 including means for sensing when the trailing end of the strip material leaves the coiler, said sensing means including a tachometer generator connected to the coiler, means for detecting a drop in the output of said tachometer generator, and means coupled to the output of said detector for causing said mill to decelerate from said intermediate speed to said preset low speed.

4. The apparatus of claim 3 including means coupled to said detecting meas for separating the rolls of said rolling mill when the end of the strip material leaves said payoff reel.

5. The apparatus of claim 2 wherein the strip material is in engagement with a roll before it passes into the mill, a second roll movable into engagement with the strip directly opposite the first-mentioned roll to maintain tension in the strip after its trailing end has left the payoff reel, and means for moving said second roll into engagement with the strip when the speed of the mill has decelerated to said intermediate speed.

'6. The apparatus of claim 1 wherein the length of material remaining on the payolt reel is calculated from a consideration of the inner diameter of said coil of strip material, the outer diameter of the coil of strip material and the gage of the strip material entering the rolling mill.

7. The apparatus of claim 6 wherein the outer coil diameter is calculated from a consideration of the rotational speed of the payolf reel and the velocity of the strip material entering the rolling mill.

References Cited UNITED STATES PATENTS 3,151,507 10/1964 Canova et a1. 72--205X 3,214,110 10/1965 Ross 24275.51X 3,421,708 1/1969 Nicholson et a1. 242-57 MILTON S. MEHR, Primary Examiner US. Cl. X.R. 

